Packers have been in use in oil and gas wells for many years. A packer is generally used to seal off down hole pressure from lower well pressures above the packer. Thus, the packer may be used at a downhole location to, for example, segregate various formation strata from other regions along the well bore. A packer may also be used in the stack at the well head to provide a seal for down hole pressures so that various operations may be performed safely above the well.
A packer commonly comprises a packer element made of a polymeric material that is somehow deformed to seal between a tubular member extending through the packer and the body of the packer. The packer also may include bushings above and below the packer element to prevent extrusion of the packer element. The bushings above and below the packer element also center the tubular member and provide long wear life for the packer element.
Although the packer element is made of a flexible polymeric material, movement of the tubing through the packer abrades away the inner surface of the packer requiring eventual replacement. Sufficient permanent deformation of the packer element will cause the packer to leak by and the packer element must therefor be replaced. Replacement of the packer elements has been shown to be an expensive and often dangerous operation since the packer must be uncoupled from the stack at the well head.
The use of two stripper/packers in tandem in the stack at the well head has become routine practice in the art. The use of tandem packers minimizes down time and offers greater safety and flexibility to operations. The upper packer is mounted below the injector head in the usual manner. The lower packer is then mounted directly beneath the upper packer. In this configuration, the lower packer is generally energized to seal the wellbore around the tubing when the upper packer becomes worn. Once the lower packer is energized, the tubing operations continue as normal until it is convenient to replace both upper and lower packer elements.
Unfortunately, with two stripper/packers in tandem, the packer replacement evolution becomes even more difficult, requiring a great deal of time and involving even greater hazards to the maintenance personnel.
Further, the configuration of known stripper/packers includes packer elements that remain in the bore of the stripper/packer, even when the packer is in the release position. This may prove particularly disadvantageous when various accessories are attached to the tubular member, such as coiled tubing, and the tubing; must be withdrawn from the hole. When such an accessory reaches the packer element, the packer usually must be disassembled to withdraw all of the tubular member from the hole.
Thus, there remains a need for a stripper/packer in which the packer element may be replaced without the need to remove the packer from the stack. There also remains a need for a stripper/packer having a packer element and such bushings as may be required, that can be withdrawn from the bore of the stripper/packer without disassembling the packer or removing the packer from the stack.
Such a stripper/packer should be easily adaptable to stacks currently in use, be simple in construction to minimize the cost of construction and enhance the ease of maintenance. Finally, the packer must securely pack off down hole pressure and work at least as effectively as known packers.